Loosey-Goosey vs. Wound Too Tight: Comparing RNA and DNA

DNA and RNA, as we’ve seen, are both nucleic acids, but there are important differences between them. For one, their composition is a little different. RNA is made up of ribonucleotides. This has implications for the sugar-phosphate backbone, which in RNA tends to be a little more flexible than in DNA. Hence, RNA can form hairpins and loops. RNA can base-pair with itself, as nucleotides within one part of the molecule loop around to match up with those in another part. This flexibility allows RNA to take on something akin to the secondary structure seen in proteins. In fact, many biologists believe that RNA is more primitive than either DNA or protein, and that the first “chromosomes” and enzymes were both made of RNA. This ability to fold into many different shapes allows RNA to carry out many different functions in the cell, as we shall see.

Figure 9. Molecular Yoga. Thanks to the flexibility of its sugar-phosphate backbone, RNA can base-pair with itself and form complex secondary structures.